When undersea cables are to be connected into offshore structures—e.g. monotowers as used in offshore installations as foundation for Wind Turbines or into gravity platforms—there is a need to control and protect the cable from over-bending and jamming during pull-in and to protect the cable against dynamic forces during operation. It is also favorable to be able to seal off the inlet through which the cable enters the structure to prevent fresh seawater from entering the structure. The system must also enable fast installation, be safe to install and have a low risk of failure to shorten the installation time and thus the involvement of a costly cable laying vessel.
Prior art solutions have proven to be difficult to install, have a high failure rate which results in a costly installation and in some cases complete cable sections need to be replaced. The prior art solutions also do not give a proper dynamic protection during operation and problematic scouring conditions. In addition, the sealing solutions used have proven not to be reliable, and/or require timely subsea intervention with divers or remotely operated vehicles.
Known prior art systems may be built up to form an array prior to pull-in, and the cable can be pulled into the structure with the array fitted onto the cable at a fixed position, which in turn limits flexibility during the pull-in operation. Examples of known systems often involve a seal solution in which a sealing member or cone is affixed to the flexible cable, which seal or cone is arranged to be pulled into engagement with a defined interface unit arranged in the inlet into the monotower.
Known sealing arrangements have, inter alia, the following shortcomings:                1. Known arrangements require a mechanically tight fit onto the flexible cable to seal off. This is undesirable due to the fact that this may restrict the cable from moving (bending/flexing) as the cable components are compressed and restricted from individual movement when the seal is engaged onto the cable        2. The seal, when sealing onto a free flooded cable (no outer water tight jacket) commonly used in these applications, will not seal off the leaks between cable components inside the cable, hence seawater will leak into the structure through the cable itself.        3. Even a jacketed cable will be difficult to seal off when the cable is not round (the outer shape is only semi-circular, due to the larger components inside forming cross sectional diameter variations over the length of the cable.        4. The seals—when compression seals are used—may require diver (possibly un-manned remote operated vehicle) assistance or operation to engage the seals onto the cable when pulled into position        5. The mechanical lock of the array to the interface is an underwater mechanical device prone to require underwater inspection to confirm the lock is engaged.        6. When the cable is installed it is fixed and held in position at the interface to the structure—plough- and jetting— operation when protecting cable by burial into the seabed, may tension the cable, resulting in increased stress and long free span which will affect the life time of the cable.        7. The cable may not be exchanged without changing the protective system—this complicate repairs e.g. when cables are damaged by impact from undersea objects such as anchors, deflectors etc.        